Interference pigments on the basis of perlite flakes
The present invention relates to pigments, comprising a plate-like substrate of perlite which does not contain 3D twin structure particles contained in milled expanded perlite in an amount of greater than 5% by weight., and (a) a dielectric material, especially a metal oxide, having a high index of refraction; and/or (a) a metal layer, especially a thin semi-transparent metal layer; a process for their production and their use in paints, ink-jet printing, for dyeing textiles, for pigmenting coatings (paints), printing inks, plastics, cosmetics, glazes for ceramics and glass.
1. A pigment, comprising a plate-like substrate of perlite, and
(a) a layer of a dielectric material and/or
(a′) a metal layer,
wherein said plate-like substrate of perlite does not contain 3D twin structure particles in an amount of greater than 5% by weight.
2. The pigment according to claim 1 , wherein the perlite substrate has a median particle size (D 50 ) of from 15-50 microns.
3. The pigment according to claim 1 , wherein the perlite substrate has a size distribution characterized as
a D 10 of at least 5 microns,
a D 50 of between about 15 and less than 50 microns, and
a D 90 of over 35 to less than 85 microns.
4. The pigment according to claim 3 , wherein the perlite substrate has a size distribution characterized as
a D 10 of 5 to 15 microns,
a D 50 of 20 to 40 microns, and
a D 90 of 50 to 70 microns.
5. The pigment according to claim 1 , wherein the dielectric material is a metal oxide of high refractive index, which is selected from TiO 2 , ZrO 2 , Fe 2 O 3 , Fe 3 O 4 , Cr 2 O 3 , ZnO or a mixture of these oxides or an iron titanate, an iron oxide hydrate, a titanium suboxide or a mixture and/or mixed phase of these compounds.
6. The pigment according to claim 5 , wherein the pigment comprises in addition (b) a metal oxide of low refractive index, wherein the difference of the refractive indices is at least 0.1.
7. The pigment according to claim 6 , wherein the metal oxide of low index of refraction is SiO 2 , AI 2 O 3 , AIOOH, B 2 O 3 , or a mixture thereof, wherein alkali or earth alkali metal oxides can be contained as additional component.
8. The pigment according to claim 1 which has the following layer structure:
perlite
TiO 2
SiO 2
TiO 2
perlite
TiO 2
SiO 2
Fe 2 O 3
perlite
TiO 2
SiO 2
TiO 2 •Fe 2 O 3
perlite
TiO 2
SiO 2
(Sn,Sb)O 2
perlite
(Sn,Sb)O 2
SiO 2
TiO 2
perlite
Fe 2 O 3
SiO 2
(Sn,Sb)O 2
perlite
TiO 2 •Fe 2 O 3
SiO 2
TiO 2 •Fe 2 O 3
perlite
TiO 2
SiO 2
MoS 2
perlite
TiO 2
SiO 2
Cr 2 O 3
perlite
Cr 2 O 3
SiO 2
TiO 2
perlite
Fe 2 O 3
SiO 2
TiO 2
perlite
TiO 2
Al 2 O 3
TiO 2
perlite
Fe 2 TiO 5
SiO 2
TiO 2
perlite
TiO 2
SiO 2
Fe 2 TiO 5 /TiO 2
perlite
TiO suboxides
SiO 2
TiO suboxides
perlite
TiO 2
SiO 2
TiO 2 /SiO 2 /TiO 2 + Prussian Blue
perlite
TiO 2
SiO 2
TiO 2 /SiO 2 /TiO 2
perlite
TiO 2 /SiO 2 /TiO 2
SiO 2
TiO 2 /SiO 2 /TiO 2 ,
wherein tin dioxide can be deposited before titanium dioxide.
9. The pigment according to claim 1 wherein the perlite core has an Fe 2 O 3 content of less than 2%, especially 0%.
10. The pigment according to claim 1 comprising a mixed layer of Al 2 O 3 /TiO 2 , or MgO/TiO 2 , or a dielectric layer/a metal layer/a dielectric layer.
11. The pigment according to claim 1 wherein the perlite flakes have an average thickness of <2 μm, especially of from 200 to 1000 nm, very especially from 200 to 600 nm.
12. A pigment mixture, comprising two different components A and B, wherein
component A is the pigment according to claim 1 , and
component B is an organic, inorganic pigment, or an effect pigment.
13. A process for producing the interference pigment according to claim 1 , by coating perlite flakes, which does not contain 3D twin structure particles in an amount of greater than 5% by weight, with one or more metal oxides in a wet process by hydrolysis of the corresponding water-soluble metal compounds, by separating, drying and optionally calcinating the pigment thus obtained, or
by suspending perlite flakes in an aqueous and/or organic solvent containing medium in the presence of a metal compound and depositing the metal compound onto perlite flakes by addition of a reducing agent.
14. A method of using the pigments according to claim 1 comprising incorporating the pigments in paints, ink-jet printing, for dyeing textiles, for pigmenting coatings, printing inks, plastics, cosmetics, glazes for ceramics and glass.
15. Paints, printing inks, plastics, cosmetics, ceramics and glass, which are pigmented with a pigment according to claim 1 .